1. Field of the Invention
The present invention relates to an anionic polymerization method for a styrene derivative containing pyridine as a functional group, and more particularly, to the anionic polymerization method in which molecular weight and molecular weight distribution can be controlled.
2. Description of the Related Art
Styrene-based monomers, unlike other monomers, are capable of being polymerized by radical, cationic or anionic polymerization due to a resonance effect of a phenyl group. Also, a synthesized polystyrene-based polymer can be modified to have various characteristics and is easily processed. Consequently, polystyrene-based monomers are being widely researched industrially and theoretically and are being commercialized.
However, in the anionic polymerization method for a styrene derivative, when the styrene derivative has a functional group such as a hydroxyl group, amine group or sulfur group, many side reactions occur during anionic polymerization due to high reactivity of an activated carbanion. Specifically, when a styrene derivative having an electron donor group as a functional group, such as —CH3, —OCH3, —NH2, or —N(CH3)2, in a para position is polymerized by anionic polymerization, polymer yield becomes low or molecular weight and molecular weight distribution of the polymer cannot be controlled due to side reactions resulting from high carbanion reactivity.
To solve these problems, anionic polymerization methods for various styrene derivatives have been developed.
Anionic polymerization methods have been disclosed in Seiichi Nakahama and Akira Hirao, Prog. Polym. Sci., 1990, 15, 299; Akira Hirao, Surapich Loykulnant, Takashi Ishizone, Prog. Polym. Sci., 2002, 15, 299; T. Ishizone, G Uehara, A. Hirao and S. Nakahama, Macromolecules, 1998, 31, 3764; T. Ishizone, T. Utaka, Y. Ishino, A. Hirao and S. Nakahama, Macromolecules, 1997, 30, 6458; and T. Ishizone, G Uehara, A. Hirao, S. Nakahama and K. Tsuda, Macromolecules, 1998, 31, 3764. These methods include: modifying styrene-based monomers having an amine group, hydroxyl group, ketone group, carboxyl group or sulfur group at a para position with an appropriate protective group such as trimethylsilyl, t-butyldimethylsilyl, oxazoline or an ester compound, polymerizing the modified styrene-based monomer by anionic polymerization, and then releasing the protective group from the functional group.
Other anionic polymerization methods have been disclosed in Christian Schade, Macromol. Chem. Phys., 1999, 200, 621; Y. S. Cho, J. S. Lee, Macromol. Rapid Commun. 2001, 22, 8, 638; and R. P. Quirk and Y. Lee, J. Polm. Sci. Part A, 2000, 38, 145. In the methods, the anionic polymerization is performed after reducing the reactivity by forming a complex and coordinate covalent bond with an additive such as lithium chloride, diethyl zinc or dibutyl magnesium. However, in these conventional methods, it is difficult to completely remove impurities from solid monomers, resulting in reduction of activity of an initiator due to the remaining impurities in the solid monomers. In addition, since the anionic polymerization is generally performed at low temperature, solid monomers may have a problem of solubility.
Since a pyridine derivative is capable of forming a complex with various metallic compounds including ruthenium, iridium or platinum, it is widely applied in research on photoconductivity and organic electroluminescence devices.
As the prior art related to the pyridine derivative, Maria C. DeRosa, Derek J. Hodgson, Gary D. Enright, Brian Dawson, Christopher E. B. Evans, and Robert J. Crutchley, J. AM. CHEM. SOC., 2004, 126, 7619; Albertus J. Sandee, Charlotte K. Williams, Nicholas R. Evans, John E. Davies, Clare E. Boothby, Anna Kohler, Richard H. Friend, and Andrew B. Holmes, J. AM. CHEM. SOC., 2004, 126, 7041; M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S. R. Forrest, Appl. Phys. Lett., 75, 4 (1999); Raymond C. Kwong, Sergey Lamansky, and Mark E. Thompson, Adv. Mater., 2000, 12, 1134; K. Dedeian, P. I. Djurovich, F. O. Garces, G Carlson, R. J. Watts, Inorg. Chem., 1991, 30, 1687-1688 disclose studies concerning an energy transfer phenomenon using an organic electroluminescence device to which a monomolecular complex synthesized of phenyl pyridine or a phenyl pyridine derivative with a metallic compound including iridium is applied. However, when such an organic electroluminescence device is formed using organic monomolecules, the organic monomolecules are decomposed due to heat generated in the device or are aggregated together.
In order to solve the problems of decomposition of the organic monomolecules due to heat generated in the device and aggregation of the organic monomolecules, a method of using a polymer of organic metal complex has been disclosed in Korean Patent No. 6660821. However, unlike the organic monomolecules having a uniform molecular weight, the polymer of organic metal complex synthesized by radical polymerization does not have a uniform molecular weight, resulting in a decrease in light emission efficiency.
The above-described anionic polymerization method for a styrene derivative and method of manufacturing an organic electroluminescence device using a pyridine derivative have several disadvantages.